Last tango in Paris

[Peter R. <php...@pe...>]

If I have a lot of tango nodes with a place attribute, and I want to find the 
5th tango in Paris, according to the Xpath definition, I should be able to do:

tango[@place="Paris"][5]

similarly, if I want to find the last tango in Paris, I should be able to do:

tango[@place="Paris"][last()]

However, I've tried numerous variations on this in the usecases testbench and 
can't get it to work - it either finds nothing or tells me there's an invalid 
number of brackets. I can find all the tangos in Paris, and the last tango, 
but not the two together. Is this a bug, something not handled (yet?), or is 
there some other notation I can use? (ok, I know I can fetch all the tangos 
in Paris and then use PHP to get the last in the array.)